The present invention relates generally to cushioning means for use by invalids, bed-ridden persons, as well as others who may be required to spend extended periods of time in either a sitting or prone position, and more specifically to body fluid absorbing cushioning means which are adapted to control and/or reduce the unit pressures exerted against the skin of such persons while so confined. The present invention is adapted primarily for reduction of the occurrence of decubitus ulcers, commonly known as bed sores, which frequently develop on the surface of skin of invalids and persons who may be bed-ridden or otherwise required to remain in a given position over extended periods of time, without being able to change positions on their own.
Normally, humans are supported by surfaces such as chairs and/or beds, and the bodies press against the skin surface with a total force generally equal to the body weight. Pressure, which may be defined as force per unit area, is exerted on the body surface over various ranges, depending upon the location, the physiology of the person, as well as the nature of the supporting surface. These pressures frequently become substantial at certain localized areas, but may be reduced when the body is floated in water or upon other cushioning means. While higher pressures can be tolerated by most individuals for short periods of time, extended exposures to high pressures at certain localized areas of the skin and/or body will eventually lead to skin necrosis and/or tissue anoxia.
The creation of decubitus ulcers or "bed sores" is an example of skin necrosis. When the blood supply to the skin is obstructed due to application of continuous pressures over extended periods of time, skin necrosis occurs, and a decubitus ulcer or bed sore may develop. Interruption of blood flow from the subcutaneous tissue over periods in excess of a few hours will generally lead to such conditions.
One way of decreasing unit pressures is to avoid concentration of forces upon limited areas. Normally, when a healthy adult male is lying supine on a bed, his total weight is substantially equally distributed across 180 square inches of body area, with the average pressure on the body surface being about 0.8 psi or 40 mm Hg. However, in practice, the weight is not equally distributed on the skin surface, but depends upon body orientation, as well as the disposition of subcutaneous bony structures or the like. In the past, work undertaken by Lindau, Greenway, and Piazza in 1965 mapped out pressure distribution on the body surface. In the accompanying drawings, FIG. 3 shows the results for the pressure distribution on a healthy adult male lying supine, with each isobar representing a constant pressure zone or area. High pressure areas are normally concentrated in the buttocks and heel for the supine position, this being the position normally assumed or occupied by bed-ridden persons.
Sitting positions result in a somewhat modified form of pressure distribution, with the highest pressure being over the ischial tuberosities and the thigh area. Typically, most of the bed sores on the bodies of wheelchair or bed-ridden patients are found around the hips where three predominant sites occur, these being the coccyx region, the trochanter of the femur, and the ischial. These areas represent, respectively, 43%, 12% and 9% of the occurrences of such ulcers and/or sores.